original development tree for Linux kernel GTP module; now long in mainline.
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/* Key to pathname encoder
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#include <linux/slab.h>
#include "internal.h"
static const char cachefiles_charmap[64] =
"0123456789" /* 0 - 9 */
"abcdefghijklmnopqrstuvwxyz" /* 10 - 35 */
"ABCDEFGHIJKLMNOPQRSTUVWXYZ" /* 36 - 61 */
"_-" /* 62 - 63 */
;
static const char cachefiles_filecharmap[256] = {
/* we skip space and tab and control chars */
[33 ... 46] = 1, /* '!' -> '.' */
/* we skip '/' as it's significant to pathwalk */
[48 ... 127] = 1, /* '0' -> '~' */
};
/*
* turn the raw key into something cooked
* - the raw key should include the length in the two bytes at the front
* - the key may be up to 514 bytes in length (including the length word)
* - "base64" encode the strange keys, mapping 3 bytes of raw to four of
* cooked
* - need to cut the cooked key into 252 char lengths (189 raw bytes)
*/
char *cachefiles_cook_key(const u8 *raw, int keylen, uint8_t type)
{
unsigned char csum, ch;
unsigned int acc;
char *key;
int loop, len, max, seg, mark, print;
_enter(",%d", keylen);
BUG_ON(keylen < 2 || keylen > 514);
csum = raw[0] + raw[1];
print = 1;
for (loop = 2; loop < keylen; loop++) {
ch = raw[loop];
csum += ch;
print &= cachefiles_filecharmap[ch];
}
if (print) {
/* if the path is usable ASCII, then we render it directly */
max = keylen - 2;
max += 2; /* two base64'd length chars on the front */
max += 5; /* @checksum/M */
max += 3 * 2; /* maximum number of segment dividers (".../M")
* is ((514 + 251) / 252) = 3
*/
max += 1; /* NUL on end */
} else {
/* calculate the maximum length of the cooked key */
keylen = (keylen + 2) / 3;
max = keylen * 4;
max += 5; /* @checksum/M */
max += 3 * 2; /* maximum number of segment dividers (".../M")
* is ((514 + 188) / 189) = 3
*/
max += 1; /* NUL on end */
}
max += 1; /* 2nd NUL on end */
_debug("max: %d", max);
key = kmalloc(max, cachefiles_gfp);
if (!key)
return NULL;
len = 0;
/* build the cooked key */
sprintf(key, "@%02x%c+", (unsigned) csum, 0);
len = 5;
mark = len - 1;
if (print) {
acc = *(uint16_t *) raw;
raw += 2;
key[len + 1] = cachefiles_charmap[acc & 63];
acc >>= 6;
key[len] = cachefiles_charmap[acc & 63];
len += 2;
seg = 250;
for (loop = keylen; loop > 0; loop--) {
if (seg <= 0) {
key[len++] = '\0';
mark = len;
key[len++] = '+';
seg = 252;
}
key[len++] = *raw++;
ASSERT(len < max);
}
switch (type) {
case FSCACHE_COOKIE_TYPE_INDEX: type = 'I'; break;
case FSCACHE_COOKIE_TYPE_DATAFILE: type = 'D'; break;
default: type = 'S'; break;
}
} else {
seg = 252;
for (loop = keylen; loop > 0; loop--) {
if (seg <= 0) {
key[len++] = '\0';
mark = len;
key[len++] = '+';
seg = 252;
}
acc = *raw++;
acc |= *raw++ << 8;
acc |= *raw++ << 16;
_debug("acc: %06x", acc);
key[len++] = cachefiles_charmap[acc & 63];
acc >>= 6;
key[len++] = cachefiles_charmap[acc & 63];
acc >>= 6;
key[len++] = cachefiles_charmap[acc & 63];
acc >>= 6;
key[len++] = cachefiles_charmap[acc & 63];
ASSERT(len < max);
}
switch (type) {
case FSCACHE_COOKIE_TYPE_INDEX: type = 'J'; break;
case FSCACHE_COOKIE_TYPE_DATAFILE: type = 'E'; break;
default: type = 'T'; break;
}
}
key[mark] = type;
key[len++] = 0;
key[len] = 0;
_leave(" = %p %d", key, len);
return key;
}